Foamed polyvinyl chloride compositions obtained by use of a chemical blowing agent in plasticized polyvinyl chloride compositions are described in U.S. Pat. No. 3,432,452; volatile solvents having a plasticizing action on polyvinyl chloride in making cellular compositions is described in U.S. Pat. No. 2,737,503; in U.S. Pat. No. 2,901,466 a hydrocarbon or halogenated hydrocarbon solvent is used in place of a plasticizer; and in U.S. Pat. No. 3,261,785 where polyvinyl chloride is cross-linked with a polysulfonazide cross-linking agent which may be used to make foams thereof whereby the cross-linking must occur before the foam collapses. Another technique for providing molded cellular polyvinyl chloride using a polyisocyanate and blowing agent is described in U.S. Pat. No. 3,200,089.
The procedures and formulations of the prior art have not been satisfactorily applied to form extruded expanded rigid vinyl chloride plastics with the desired balance of processing and physical properties. For rigid extrusions plasticizers are not desired and solvents introduce handling and processing problems. Extruded expanded products produced in accordance with known methods often have large non-uniform cell structure and density has been difficult to control. Further, the prior art formulations would not form low specific gravity products having enough hot strength for extrusion processes nor for pulling through sizing equipment. For applications where profile extrusion must be uniformly sized, such formulations have not been satisfactorily used.